“Lime” is a general term used for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Lime is used in large quantities as building and engineering materials (including limestone products, concrete and mortar) and as chemical feedstocks, among other uses. Lime is typically derived from mined limestone or chalk, which are composed primarily of calcium carbonate. These rocks may be crushed or pulverized and chemically altered through various processes. “Burning” (calcination) converts lime into the highly caustic material known as “quicklime” (calcium oxide, CaO). Through subsequent addition of water, quicklime is converted into the less caustic (but still strongly alkaline) slaked lime or hydrated lime (calcium hydroxide, Ca(OH)2). The process of converting quicklime to slaked lime or hydrated lime is called slaking of lime.
The chemical reactions describing the production of high calcium or dolomitic based lime hydrate are as follows:

Quite often the terms Hydrated Lime and Slaking are used interchangeably; however there is a definite and distinct difference between the two terms. Hydrated Lime is defined as a process whereby approximately stoichiometric amounts of water and lime react to form a product, hydrate, which is a dry powder; i.e. it contains less than 1% free moisture and is handled as a powder. In contrast, slaking is defined as a process whereby lime is reacted with an excess amount of water to form a lime slurry which is handled as a liquid. Hydrated lime is a very well-known and understood material that has been used for many years as an additive into many different industrial applications. It is formed when quicklime or calcium oxide (CaO) comes into contact with water. When water is added to quicklime an exothermic reaction takes place which converts the CaO to Ca(OH)2. This exothermic reaction is known to drive off the water the calcium oxide reacts with in a very extreme rise in temperature while releasing evaporated water. Once the material has reacted it becomes very stable and is thereafter used in many applications from civil engineering work, additives in food, to stabilize soils and foundations, and the like.
The quality of raw lime materials vary with the quality of the rock formations from which it is mined. Limestone deposits differ in quality by many aspects. One of the most measurable differences is the magnesium content of the deposit. As magnesium content increases to higher levels, a different grade of lime is the end result. This high magnesium content lime is called “dolomitic lime” and is preferred in the production of certain end products.
The production of hydrated lime starts at a limestone quarry. The limestone, CaO3, is mined as a mineral from the characteristic quarry for the desired final product use. The limestone is processed to a fineness required for the energy intensive kiln process wherein CO2 is driven off and the result is a fine white product comprised mostly of CaO and a percentage of MgO (dependent on the mineral deposit within the quarry). Since the CaO and MgO are very reactive with water, the material is either immediately hydrated on site at a hydration facility or stored in a low moisture environment.
There are many lime hydration facilities throughout the world. Although there are many specific and unique ways to hydrate specific quicklimes, the most common ways involve one of two types of process. The first is a non-pressure environment which is most commonly used for high calcium quicklime where the magnesium oxide content is less than 7%. The second involves high pressure process wherein the higher magnesium oxide content limes (where the magnesium oxide content is more than 7%) are hydrated more fully than without the use of pressure.
The amount of pressure can be modified to aid in the hydration of the MgO, which is harder to hydrate than CaO. In addition, the amount of water that can also be modified to aid in the hydration process. Slaking is often used for the process which involves the use of greater than stoichiometric amounts of water beyond what is needed for the full reaction and results in a liquid-lime slurry.
The improved process is a modification to the dry hydration process.